When researchers examined the areas of the brain that were most active when people were looking at healthy or unhealthy foods, they found the reward centres of the brain were activated when sleep-deprived study volunteers saw pictures of unhealthy foods.
"We found regions associated with reward and motivation - those that are involved with addiction and pleasure-seeking behaviours - were more strongly activated in the short-sleep phase," said Marie-Pierre St-Onge, a research associate at St. Luke's Roosevelt Hospital Center and an assistant professor at Columbia University's Institute of Human Nutrition in New York City.
A second small study from the same meeting didn't find a large difference in the activation of the brain's reward centres in people who were tired. The researchers from the University of California, Berkeley did, however, find significantly impaired activity in an area in the frontal lobe of the brain. This area of the brain helps control behaviour and make complex choices. When people were sleep-deprived and then presented pictures of unhealthy foods, this area of the brain didn't respond well, which would make choosing healthy foods more difficult.
How the study was done
The study included 16 healthy young adults who underwent functional magnetic resonance imaging (fMRI) once after a full night of sleep and then again after 24 hours of sleep deprivation. They were asked to rate their desire for 80 different foods during each test.
St-Onge's study included 25 normal-weight men and women who underwent fMRI after five nights of restricted sleep (four hours a night) and then again after five nights of being allowed to sleep for nine hours.
While they were in the fMRI scanner, they were shown pictures of healthy foods, such as fruits, vegetables and oatmeal; unhealthy foods, such as candy or pepperoni pizza; and nonfood items, such as office supplies.
They found that unhealthy foods activated areas of the brain considered reward centers only in people whose sleep was restricted. When the same people were allowed to rest a full night, they had no such activation in the brain's reward center when they saw the unhealthy foods.
"I think it's related to cognitive control," St-Onge explained. "Your guard is somewhat down when you're tired and sleep deprived. Even though you know you probably shouldn't eat certain foods, when you're tired you might just decide to go for it."
Registered dietician Samantha Heller said she was not surprised by the studies' findings.
Sleepy bodies crave energy
"It makes sense that when you are fatigued, your body would want calorie-dense foods that give you quick energy," said Heller, clinical nutrition coordinator at the Center for Cancer Care at Griffin Hospital in Derby, Conn. "In an evolutionary sense, doing so would provide an advantage because you do get a momentary lift when you eat."
In today's society, the foods people often turn to for a quick shot of energy are processed carbohydrates, rather than a piece of fruit. But, she said, that momentary lift from processed foods won't last long, and trying to eat to make up for sleep deprivation just won't work.
A better choice is to keep healthy foods around, in both your home and workplace, so it's easy to reach for a healthy option, Heller said.
St-Onge said a clear message from her study is that it's important to get enough sleep every night. She suggested between seven and eight hours nightly.
"This is especially important if you're trying to lose weight," she said, because you may choose the wrong foods if you don't get enough sleep.
Because this study was presented at a medical meeting, the data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.
Learn more about the importance of sleep from the American Psychological Association.
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